24 



BULLETIlSr 75, U. S. DEPAETMENT OF AGEICULTURE. 



the hot sunshine automatic tripping took place quickly and could 

 easily be observed. These observations remove any possible doubt as 

 to the movement being automatic. It will take place, however, only 

 when the sun's heat is intense. It now seems clear that automatic 

 tripping is induced mainly by hot simshine, though it is not proved 

 that flowers continually in the sunshine will be tripped to the same 

 extent as those alternately in the shade and exposed. 



POLLINATION IN RELATION TO THE RUPTURE OF THE STIGMATIC 



CELLS. 



BurkiU's conclusion that the stigma is not susceptible of pollination 

 until the stigmatic cells have been ruptured has ah^eady been men- 

 tioned. To test this matter further, the following investigations 

 were conducted by J. M. Westgate in the greenhouse at Washing- 

 ton, D. C, by W. J. Morse at Arlington farm, Virginia, and by 

 M. W. Evans at Pullman, Wash. Two methods were used. In the 

 first, the standard was removed and the flower then tripped. The 

 results of the experiment with this method at the thi-ee places 

 mentioned are shown in Table XIV. 



Table XIV. — The setting of alfalfa pods hy flowers tripped after removing the standard. 





Place. 



Year. 



Num- 

 ber of 

 plants. 



Number 

 of flowers 

 tripped. 



Ntunber 

 of pods 

 formed. 



Flowers 



bearing 



pods. 



Number of seeds. 



Observer. 



Total. 



Average 

 per pod. 



Westgate.. 



Washington, D.C. 



Arlington farm 



...do 



1908 

 1908 

 1909 

 1909 



18 

 5 

 5 



468 

 123 

 23 

 113 



74 

 28 

 10 

 14 



Per cent. 

 15.8 

 22.8 

 43.4 

 12.4 







Morse . . 



37 

 16 



1.3 



Do 



1.6 



Evans 



Pullman, Wash... 













These results show clearly that the mechanical effect of the stigma 

 striking the standard is not necessary to insure fertilization. Morse 

 also tripped flowers, allowing the stigma to strike the standard. 

 In these experiments, 76 flowers in 1908 produced 18 pods, or 23.7 

 per cent, and 42 flowers in 1909 produced 22 pods, or 52.4 per cent. 

 These figures are but slightly larger than where the standard was 

 removed. When the stigma was allowed to strike a piece of wood 

 used in tripping, 21 flowers in 1908 produced 3 pods, and 12 flowers 

 produced 4 pods — percentages 14.3 and 33.3, respectively. Though 

 the numbers of flowers used in the last test were small, the results 

 do not indicate that any additional benefit was secured. 



The second method was to remove the standard and then sever 

 the keel at the base with a razor. The column thus retained its posi- 

 tion in the keel unchanged after tripping. The results of the ex- 

 periment with this method are shown in Table XV. 



